Image information, be it color or black and white, is commonly generated in a bitmap format at a particular resolution K.times.L.times.b, corresponding to a desired printer output, where K is a number of spots per unit of length in one dimension, L is a number of spots per unit length in the other dimension, and b is the depth of each pixel, in number of levels. This bitmap is present for every color separation of the output device; i.e., 4 bitmaps for a 4-color output device, 3 bitmaps for a 3-color output device, 2 bitmaps for a 2-color output device and 1 bitmap for a black and white output device.
Typically, a black and white output device will render a bitmap of image data at 600 spots per inch (spi) in both dimensions, at a one bit pixel depth giving 2 levels. In contrast, the resolutions of the images being generated for today's printers are diverse and are usually greater than the native resolution of the printer as a result of PCs, scanners, decomposers, and image processing techniques becoming more robust and sensitive. This growth in diversity on the image generation side of the system has not been replicated by the printers. Thus, to properly print an image, the resolution of the image must be converted to that of the printer's resolution.
This presents a problem. It has been suggested to simply convert the image to the new resolution using scaling methods, but such a solution can cause loss of information content in the converted image, especially when the resolution of the image is greater than the printer's resolution. Therefore, it is desirable to provide a resolution conversion process which converts the image to the printer's resolution, but also retains the information content of the original image.